The Sharp Compet 229 is about as generic
an office calculator as an early 1974 machine can get. Calculators like these
dutifully churned through numbers for places like the North Carolina
Department of Motor Vehicles, which is where this machine served out its
useful life. Fortunately, rather than being tossed in the trash, as was the
fate of so many calculators that outlived their usefulness, this one ended
up at a surplus auction and was spared the indignity of ending up in a landfill.

Internal shot of Sharp Compet 229

This Compet 229, one of many in the line
of Compet electronic calculators that Sharp produced for years on end, was
built in the early 1974 timeframe, based on date codes from late '73 through
the 1st week of 1974 on the IC's within the machine. It uses a two-chip
(HD32128 and HD32129) calculator chipset made by Hitachi for the calculating
brains of the machine. For displaying the results, a Hitachi-made (H1831B)
Panaplex-style display module does the job, with discrete transistor-based
driver circuitry. Five Hitachi HD3233 small-scale integration chips provide
glue functions, both on the main calculator board, and also on a small
circuit board attached to the keyboard assembly.

The Panaplex-style display of the Compet 229

The Compet 229 provides the function
of a four-function office calculator with a full-function memory. The
machine calculates results to 12-digits, with an apparent 13th
guard digit (for round-off funcionality), and uses fixed (but flexible)
decimal point logic, with switch-selectable settings of 0, 1, 2, 3, 4, or
6 digits behind the decimal point. I say flexible, because the machine will
automatically back off on the number of digits displayed behind the decimal
point if the whole part of the number is too large to be displayed with the
selected number of digits behind the decimal point. At the far right end of
the display module, a special digit position contains indicators for
negative number and memory register in use. A switch on the keyboard panel
selects round-off or truncate mode for the least-significant digit in
results. The calculator provides a constant function (when the "K" key is
in the 'locked down' position) for multiplication and division only.
The "RC" key swaps the order of operands in multiply and divide operations.

Overflow or error (divide by zero) Indication

Overflow or error conditions
are indicated by the display cleared with only decimal points lit.
The "C" key must be used to reset any overflow/error condition.
The "CE" key provides a "Clear Entry" function to allow correction of
incorrectly entered numbers. The machine provides leading zero suppression,
which, combined with a small slider under the display window (that is used
to group the display digits in groups of three) makes for easy reading and
transcription of the results of calculations.

Detail of the Sharp Compet 229 Keyboard Assembly

The Compet 229 uses a reliable magnetic
reed-switch style keyboard, with hand-wired connections to an edge-connector
which plugs into the main board of the calculator. The main board is a
single-sided printed circuit board. The power supply of the machine is
a transformer-based linear supply, with transistor-regulated voltages.

The 229 calculates a little on the
slow side. 'All nines' divided by one takes just about
3/4 of a second to complete, making it one of the slower electronic
calculators in the museum. The display is blanked during calculation.